1. Field of the Invention
In recent years, the following technique for production of three-dimensional objects has been widely used: Design by CAD-programs and then transformance of the design into objects by stereolithography. The present invention relates to a novel and improved process for the production of 3-D objects by means of stereolithography using laser hardening.
2. Description of the Related Technology
Until today, stereolithography has been limited to the production of design samples. Hardening is done by an ultraviolet laser which spreads over a basin filled with fluid resin and hardens the resin at selected areas. The objects so manufactured serve as samples for testing and checking purposes e.g. in respect of their installation characteristics and handling. These objects possess only minor strength and their use is limited as mentioned above.
An aim of the invention is to improve the process in order to manufacture objects with qualities that could not be reached with the aforementioned method, e.g. objects having high strength, thermal conductivity, specific surfaces and so on.
The invention solves the problem by use of a specific technique for production of three-dimensional objects by stereolithography and laser hardening. Prior to or during laser light action, particles which define physical and/or mechanical characteristics of the object-to-be-produced will be added into the resin fluid in order to achieve a liquid fluid-resin-particle-mixture. By action of laser light, the particles will be combined with the hardened resin and/or will be compound with themselves.
There are numerous types of particles and numerous ways of adding them into the resin. Generally, it is possible to add particles in solid and/or liquid and/or gaseous condition into the fluid resin and distribute them therein. Moreover, the possibilities to modify such particles are nearly unlimited: e.g. use of particles with gas bubbles at their surface or at their inside to achieve an isolation effect, or use of particles which transform during laser light action into gaseous condition and thereby produce a hollow in the object-to-be-produced. Addition of particles of nanomaterial e.g. in form of nano metal or nano fluids is preferable if particular characteristics which result from the nanomaterial shall be achieved, e.g. a high conductivity (electric, magnetic or thermal).
A high thermal conductivity will be achieved, if mainly liquid resin particles, which lead to high conductivity after hardening, are added. When pouring in, the particles can be covered with a thin separation layer which prevents the particles from dissolving in the resin fluid.
Good results can be achieved if the particles are covered with a layer (preferably a liquid) which activates their connection with the resin or with themselves. It is possible to cover the particles with material, adapted for laser sintering, and include it in the resin fluid in high concentration or in agglomerating condition.
To evenly distribute the particles within the resin fluid, the resin-fluid-particle-mixture will be treated with ultrasonic waves which evenly distributes and preserves this condition.
One preferred mode of the process is to surface-activate particles prior to adding them into the resin fluid. Activation can be done in differentways. The particles can, for example, be plasma-activated. Particles of metal or a metal compound will normally be chemically activated. Activation can also be achieved by specific nano materials, preferably in liquid condition.
It is advantageous for many objects to have particular qualities at a particular place in the object, e.g. if the surface of the object shall be of high thermal conductivity or pollution-proof. In such a case, it is possible to selectively add the particles so as to receive a higher concentration of particles at specific parts of the object. Selective addition of particles may done analoguous to ink or silk screen printing techniques. It is also possible to subject non-metal particles before hardening of the resin-fluid-particle-mixture to an electromagnetic orientation process.
In some cases it can be of advantage to treat the resin fluid twice with laser light action, directly one after another, the first of which will be performed with reduced energy. This method is recommendable if gaseous particles are added into the resin fluid. By the first energy-reducing initial laserbeam, a higher temperature of the mixture is achieved and the size of the gas bubbles will increase. The directly succeeding xe2x80x9cnormalxe2x80x9d laser treatment will do the final hardening. It is, however, also possible to dissolve gaseous particles in the resin fluid and to transform them partially into gas bubbles by initial laser beam. Size of gas bubbles can be varied by varying the intensity and/or duration of the laser treatment.
A considerable advantage of the objects produced by the above described method is their recyclability. Objects can be re-separated into their original materials. Recycling can be done by grinding the object with liquid nitrogen and sorting the resin and particles.